Ferroelectric memory devices use ferroelectric materials to store information. These materials can store information by retaining a polarization state after exposure to an electric field.
Some of these devices have a sheet of ferroelectric material layered over a conductive layer. A writing device, such as a plate or point, can be used to expose regions of the ferroelectric sheet to an electric field. The plate or point acts to create an electric field in the region by placing a charge over the region opposite the conductive layer. This region is polarized, the polarization state is then retained after the electric field dissipates.
The surface charge of the region can later be read by a reading device. The reading device moves another plate or point over the ferroelectric sheet, thereby reading the polarization state of the regions.
Many of these ferroelectric memory devices use polycrystalline ferroelectric materials to store information. These polycrystalline materials have a grain structure that can make reading their polarization state difficult. This is especially true when reading small regions of the polycrystalline materials because each small region often has a small number of grains. For a region having few grains, the noise from the grain structure interferes with accurate measurement of the region's polarization state.
Also, many ferroelectric memory devices are physically integrated with integrated circuits (ICs). Polycrystalline ferroelectric materials are often fabricated at fairly high temperatures, which can cause problems with neighboring ICs.
Others of these ferroelectric memory devices have single-crystal ferroelectric materials. These single-crystal materials are less likely to have problems associated with noise, but have other significant problems. First, fabricating single-crystal ferroelectric materials is relatively expensive. Second, fabricating them is often performed at high temperatures. These high temperatures can cause significant problems with neighboring ICs. If formed first and then added to an IC, the single crystals may be placed into the IC but this is difficult and expensive, especially if they are small.
The same numbers are used throughout the disclosure and figures to reference like components and features.